This application is based on application No. 11-187194 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a scanning optical system and a laser scanning apparatus using the scanning optical system, and more particularly, to a laser scanning apparatus suitable for use as a writing optical apparatus such as a laser beam printer.
2. Description of the Prior Art
Conventionally, in the field of scanning optical systems, a technology has been proposed to form a laser scanning optical system for scanning a surface at a substantially constant speed by use of a so-called toroidal mirror. An example is described in U.S. Pat. No. 5,353,047. Moreover, a technology has been proposed to form a scanning optical system that realizes high resolution although being small in size and low in cost by use of two rotationally symmetrical mirrors, for example, as described in Japanese Laid-open Patent Application No 08-220440.
However, in the above-described structures of the conventional scanning optical systems, only movement and rotation of the rotationally symmetrical surfaces are provided as the degree of freedom for absorbing the asymmetry in the sub scanning direction associated with optical path separation, and it is difficult to simultaneously resolve the problems of so-called bow and out-of-shape beam due to the asymmetry in the sub scanning direction.
An object of the present invention is to provide an improved scanning optical system.
Another object of the present invention is to provide a scanning optical system having better imaging performance although using a mirror.
The above-mentioned objects are achieved by a scanning optical system comprising: a first optical functional surface being a reflecting surface having a xe2x80x9ctwistedxe2x80x9d configuration; and a second optical functional surface having a xe2x80x9ctwistedxe2x80x9d configuration different from the xe2x80x9ctwistedxe2x80x9d configuration of the first optical functional surface.